Miscarriage (Early Pregnancy Loss)

Miscarriage (Early Pregnancy Loss) is a topic covered in the 5-Minute Clinical Consult.

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  • Miscarriage, also known as spontaneous abortion (SAb), is the failure or loss of a pregnancy before 13 weeks’ gestational age (WGA).
  • Related terms
    • Anembryonic gestation: gestational sac on ultrasound (US) without visible embryo after 6 WGA
    • Complete abortion: entire contents of uterus expelled
    • Ectopic pregnancy: pregnancy outside the uterus
    • Embryonic or fetal demise: cervix closed; embryo or fetus present in the uterus without cardiac activity
    • Incomplete abortion: abortion with retained products of conception, generally placental tissue
    • Induced or therapeutic abortion: evacuation of uterine contents or products of conception medically or surgically
    • Inevitable abortion: cervical dilatation or rupture of membranes in the presence of vaginal bleeding
    • Recurrent abortion: ≥3 consecutive pregnancy losses at <15 WGA
    • Threatened abortion: vaginal bleeding in the 1st trimester of pregnancy
    • Septic abortion: a spontaneous or therapeutic abortion complicated by pelvic infection; common complication of illegally performed induced abortions
  • Synonym(s): miscarriage; early pregnancy loss
    • Missed abortion and blighted ovum are used less frequently in favor of terms representing the sonographic diagnosis.


Predominant age: increases with advancing age, especially >35 years; at age 40 years, the loss rate is twice that of age 20 years.

  • Threatened abortion (1st-trimester bleeding) occurs in 20–25% of clinical pregnancies.
  • Between 10% and 15% of all clinically recognized pregnancies end in SAb, with 80% of these occurring within 12 weeks after last menstrual period (LMP) (1).
  • When both clinical and biochemical (β-hCG detected) pregnancies are considered, about 30% of pregnancies end in SAb.
  • One in four women will have a SAb during her lifetime (1).

Etiology and Pathophysiology

  • Chromosomal anomalies (50% of cases)
  • Congenital anomalies
  • Trauma
  • Maternal factors: uterine abnormalities, infection (toxoplasma, other viruses, rubella, cytomegalovirus, herpesvirus), maternal endocrine disorders, hypercoagulable state

Approximately 50% of 1st-trimester SAbs have significant chromosomal anomalies, with 50% of these being autosomal trisomies and the remainder being triploidy, tetraploidy, or 45X monosomies.

Risk Factors

Most cases of SAb occur in patients without identifiable risk factors; however, risk factors include the following:

  • Chromosomal abnormalities
  • Advancing maternal age
  • Uterine abnormalities
  • Maternal chronic disease (antiphospholipid antibodies, uncontrolled diabetes mellitus, polycystic ovarian syndrome, obesity, hypertension, thyroid disease, renal disease)
  • Other possible contributing factors include smoking, alcohol, cocaine use, infection, and luteal phase defect.

General Prevention

  • Insufficient evidence supports the use of aspirin and/or other anticoagulants, bed rest, hCG, immunotherapy, progestogens, uterine muscle relaxants, or vitamins for general prevention of SAb before or after threatened abortion is diagnosed.
  • By the time hemorrhage begins, half of pregnancies complicated by threatened abortion already have no fetal cardiac activity.
  • Recurrent miscarriage: Women with a history of ≥3 prior SAbs may benefit from progestogens (OR 0.39, 95% CI 0.21–0.72) (2)[A].
  • Antiphospholipid syndrome: The combination of unfractionated heparin and aspirin reduces risk of SAb in women with antiphospholipid antibodies and a history of recurrent abortion (RRR 46%, 95% CI 0.29–0.71).

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